The present invention relates to process for reforming the edge of a container opening cover and in particular to a method and apparatus for reforming the edge of a two piece or three piece shell before the shell is seamed to a container body to reduce scalloping or other irregularities in the shell perimeter.
A number of processes are used for closing or covering a container opening such as in the process of manufacturing and filling a two piece or three piece beverage or food container. Typically, a container body has a side wall which is substantially cylindrical with at least one substantially circular rim defining an open end of the container body. In a number of previous configurations, a container end shell which is substantially disk-shaped (although it may have various recesses, scores, indicia and the like) has a perimeter substantially the same shape as the container opening rim. The container may be closed by seaming the angular region of the shell perimeter to the rim region of the container body such as by a double seaming operation, as known to those of skill in the art.
In many situations, it is strongly preferred to maintain, at any circumferential position along the shell perimeter or the container body rim, a sufficient radial extent of the annular shell portion which is to be seamed, in proximity with the can body rim portion to which it is to be seamed, so as to assure that the seam will have structural integrity, form a desired, preferably hermetic, seal between the shell and the container body and will be able to withstand certain shocks or impacts such as those often encountered during transport, retailing, sale and normal end-user use.
A number of procedures often involved in providing or forming the shell 912 (FIGS. 9A and 9B) result in a shell whose perimeter departs from perfect regularity (typically, departs from perfect circularity) such as when portions of the shell periphery are somewhat indented or scalloped, as compared to a perfect circular form. These departures of the shell periphery from ideal regularity contribute to container configurations in which the amount of material provided to achieve the seaming operations exceed the materials that are, at least theoretically, minimally required. For example, when, to achieve the desired seaming integrity, an annular region with a radial extent of X is needed, if the shell edge is scalloped inwardly by radial extent equal to Y, the shell must be provided with an annular seaming region having a nominal or intended radial extent of about X+Y (so that, even in portions of the annular region where scalloping occurs, the radial extent will be at least equal to the nominal or intended extent of X+Y, less the maximum scalloping defect of Y, to provide a guaranteed minimum radial extent of X, as desired).
For this reason, some shell formation and/or seaming operations provide a double seam which is larger than that which would be theoretically minimally required, in order to maintain seam integrity even in the face of an amount of shell edge scalloping. Accordingly, it would be useful to provide a procedure which can reduce or eliminate the adverse effects of scalloping on seam sizes, so as to provide for containers with rugged and integral seams but with a reduced seam size.
In many container-forming procedures, it is desirable to provide seaming regions (or other regions) of the container end closure shell which has a degree of hardness, e.g. to assist in maintaining seam integrity, regardless of normal shocks or impacts on the container. To provide for proper seaming, the shell typically must have a diameter suited to the container body rim diameter, but which also has sufficient thickness to provide and maintain a reliable seam. Accordingly, it would be advantageous to provide a shell which provides for at least regions that are hardened, particularly in the annular seaming area. It would be advantageous to provide a process for forming shells that results in at least some increase in effective shell diameter, without thinning regions of the shell to the point that structural integrity may be compromised.
The present invention involves subjecting the shell or shell blank to the application of a forming operation such as coining, spinning or die-forming at least in the periphery or seaming area of the shell, prior to the seaming operation. Preferably, if coining is used, the coining operation involves use of a die having a wall which can define the desired (typically, regular) shape of the shell periphery, so that coining may reform a shell from a shape which may have scalloped or otherwise irregular edges to a shape which has substantially regular, substantially unscalloped edges. Preferably, the present invention allows the formation of containers having a seam size smaller than the seam size provided in correspondingly-shaped containers formed by previous procedures, substantially without sacrificing integrity or durability of the seam. The coining operation preferably provides an increase in the diameter of the shell (at least some locations around the circumference) all having relatively minor effects on the thickness of the coined region. Preferably, the coining achieves a degree of work-hardening of the coined area, which may help to offset the effects of any diminution of thickness caused by the coining operation.
In one embodiment, a non-precurled, non-curled shell is transferred to a reform station. This station contains a coin die and coin punch. The coin die has the desired round finished blank diameter machined into the die face. The die cavity has a round die wall which stops the outward flow of material during the coining process. The die wall produces the blank""s final shape. During the coining process, the coining punch compresses the scalloped blank edge of the non-curled, non-precurled shell. Coining of the coined area causes the material to flow outward until it comes in contact with the die wall, forming the blanks outer diameter. This corrects the scalloped edge of the blanks and additionally work hardens the edge and increases the blank diameter. This configuration can also eliminate the need for (expensive) non-round cut edge tooling.